SUMMARY

The planned MEC-U facility will house a high intensity rep-rated short pulse laser capable of accelerating electrons and ions beyond tens of MeV during each experiment. Operation of this facility will result in activation of the instrumentation and structure in the experimental hutch. This research aims to quantify the hazards from activation over the lifetime of the MEC-U, and use this data to make informed recommendations to the project. After assuming a realistic and conservative operational pattern, the FLUKA Monte Carlo code was used to simulate the activation of the facility. Aluminum alloys 5051, 6061, and 7075 were tested for the target chamber, and ASTM A36 steel was tested against Al-6061 for the construction of the surrounding support structure. Results demonstrated that Al-7075 should not be used, as it produces residual dose rates twice as high as the other alloys. Results further demonstrated that steel could be used for the support structure, as it does not cause significantly higher dose rates in the hutch. Following material selection, additional simulations were performed to estimate the yearly effective dose that personnel could receive during operation. A set of work schedules were developed in consultation with MEC-U scientists, which were then used to integrate dose rate curves to calculate a cumulative personnel dose for each schedule. Infrequent access to the interior of the target chamber was considered separately, as well. Combining these two factors, a SLAC scientific staff member working in the MEC-U was estimated to receive 92 mrem in one year without any additional mitigations. Technicians were estimated to receive up to 114 mrem in one year. Estimates are also provided for the additional dose received from handling diagnostic equipment. The current dose estimates did not exceed the SLAC ALARA dose limit of 360 mrem/y, but safety measures and other mitigations will be subsequently considered to ensure conformity with ALARA principles.